1. Technical Field
The invention relates to pyrrole derivatives, compositions comprising such compounds, and methods of treating conditions and disorders using such compounds and compositions.
2. Description of Related Technology
Neuronal nicotinic acetylcholine receptors (nAChRs) are neurotransmitter receptors that are widely distributed throughout the central nervous system (CNS) and the peripheral nervous system (PNS) and are widely understood to play an important role in regulating CNS function. Primarily, nAChRs play a significant part of regulating the release of many neurotransmitters, for example acetylcholine (ACh), norepinephrine, dopamine, serotonin, and GABA, among others. Consequently, nAChRs mediate a wide range of physiological effects.
Twelve protein subunits of neuronal nicotinic receptors have been reported to date (Paterson, D. and Nordberg, A.: Neuronal nicotinic receptors in the human brain. Prog. Neurobiol. 2000; 61:75-111. Hogg, R. C., Raggenbass, M. and Bertrand, D.: Nicotinic acetylcholine receptors: From structure to brain function, Rev. Physiol., Biochem Pharmacol. 2003; 147: 1-46). These subunits are identified as α2, α3, α4, α5, α6, α7, α8, α9, α10; β2, β3, and β4. Of these subunits, nine subunits, α2 through α7 and β2 through β4, prominently exist in the mammalian brain. Multiple functionally distinct nAChR complexes also exist, for example five α7 subunits can form a receptor as a homomeric functional pentamer or combinations of different subunits can complex together as in case of α4β2 and α3β4 receptors. In the mammalian brain, α4β2 and α7 nAChRs are prominently found.
The role of α7 nAChR in neuronal signaling in the CNS also has been actively investigated. (Couturier, S., Bertrand, D., Matter, J. M., Hernandez, M. C., Bertrand, S., Millar, N., Valera, S., Barkas, T., Ballivet, M. A. Neuronal nicotinic acetylcholine receptor subunit (alpha 7) is developmentally regulated and forms a homo-oligomeric channel blocked by alpha-BTX. Neuron 1990; 5: 847-56). The α7 nAChRs have been demonstrated to regulate interneuron excitability, modulate the release of excitatory and inhibitory neurotransmitters, and lead to neuroprotective effects in experimental in vitro models of cellular damage (Alkondon, M., Albuquerque, E. X. The nicotinic acetylcholine receptor subtypes and their function in the hippocampus and cerebral cortex. Prog. Brain Res. 2004; 145:109-20). Also, studies support that α7 nAChRs are involved in various cognitive functions, including memory, attention, and in schizophrenia (Keller, J. J., Keller, A. B., Bowers, B. J., Wehner, J. M. Performance of alpha7 nicotinic receptor null mutants is impaired in appetitive learning measured in a signaled nose poke task. Behav. Brain Res. 2005; 162:143-52). Biophysical studies have shown that α7 subunits, when expressed in heterologous expression systems, activate and desensitize rapidly, and furthermore, exhibit relatively higher calcium permeability compared to other nAChR combinations (Dajas-Bailador, F., Wonnacott, S. Nicotinic acetylcholine receptors and the regulation of neuronal signalling. Trends Pharmacol. Sci. 2004; 25:317-24).
As such, modulating, or modifying, the activity of α7 nAChRs demonstrates promising potential to prevent or treat a variety of diseases with an underlying pathology that involves cognitive function including, for example, aspects of learning, memory, and attention, as well as schizophrenia and neurodegeneration, such as in Alzheimer's disease and other dementias (reviewed in Gotti, C., Riganti, L., Vailati, S., Clementi, F. Brain neuronal nicotinic receptors as new targets for drug discovery. Curr. Pharm. Des. 2006; 12:407-28). More particularly, the α7 nAChRs have been linked to conditions and disorders related to attention deficit disorder (ADD), attention deficit hyperactivity disorder (ADHD), Alzheimer's disease (AD), mild cognitive impairment (MCI), senile dementia, dementia associated with Lewy bodies, dementia associated with Down's syndrome, AIDS dementia, Pick's disease, as well as cognitive deficits associated with schizophrenia, among other systemic activities (for example, Martin, L. F., Kem, W. R., Freedman, R. Alpha-7 nicotinic receptor agonists: Potential new candidates for the treatment of schizophrenia. Psychopharmacology (Berl). 2004; 174:54-64). The α7 nAChRs have also been reported to slow disease progression in Alzheimer's disease (D'Andrea, M. R., Nagele, R. G. Targeting the alpha 7 nicotinic acetylcholine receptor to reduce amyloid accumulation in Alzheimer's disease pyramidal neurons. Curr. Pharm. Des. 2006; 12:677-84). Additionally, recent studies indicate that α7 nAChRs are involved in non-neuronal cell function, which supports that compounds targeting α7 nAChRs are useful for treating or preventing inflammation and inflammatory pain, septic shock, wound healing, tumor growth inhibition, angiogenesis and skin disorders as well (Ulloa, L. The vagus nerve and the nicotinic anti-inflammatory pathway. Nat. Rev. Drug Discov. 2005; 4: 673-84; Wang, H., Yu, M., Ochani, M., Amella, C. A., Tanovic, M., Susarla, S., Li, J. H., Wang, H., Yang, H., Ulloa, L., Al-Abed, Y., Czura, C. J., Tracey, K. J. Nicotinic acetylcholine receptor alpha7 subunit is an essential regulator of inflammation. Nature 2003; 421:384-8).
One well-known compound, nicotine, is known to provide enhanced attention and cognitive performance, reduced anxiety, enhanced sensory gating, and analgesia and neuroprotective effects when administered. Such effects are mediated by the non-selective effect of nicotine at a variety of nicotinic receptor subtypes. However, nicotine also produces adverse consequences, such as cardiovascular and gastrointestinal problems. Accordingly there is a need to identify subtype-selective compounds that embrace the beneficial effects of nicotine, or a nAChR ligand, while eliminating or decreasing adverse effects.
Examples of reported nAChR ligands are α7 nAChR agonists, such as PNU-282987 (Hajos, M., Hurst, R. S., Hoffmann, W. E., Krause, M., Wall, T. M., Higdon, N. R., Groppi, V. E. The selective alpha7 nicotinic acetylcholine receptor agonist PNU-282987 [N-[(3R)-1-azabicyclo[2.2.2]oct-3-yl]-4-chlorobenzamide hydrochloride] enhances GABAergic synaptic activity in brain slices and restores auditory gating deficits in anesthetized rats. J. Pharmacol. Exp. Ther. 2005; 312:1213-22). Another compound is SSR180711A (Pichat, P., Bergins, O. E., Terranova, J., Santucci, V., Gueudet, C., Francon, D., Voltz, C., Steinberg, R., Griebel, G., Scatton, B., Avenet, P., Oury-Donat, F., Soubri, P. (2004) SSR180711A, a novel selective alpha7 nicotinic receptor partial agonist III effects in models predictive of therapeutic activity on cognitive symptoms of schizophrenia. Society for Neuroscience Abstract number 583.3). Yet another compound, AR-R17779 (Van Kampen, M., Selbach, K., Schneider, R., Schiegel, E., Boess, F., Schreiber, R. AR-R17779 improves social recognition in rats by activation of nicotinic alpha7 receptors. Psychopharmacology (Berl) 2004; 172:375-83), has been reported to improve performance in rats in social recognition, water maze performance, or inhibitory avoidance models of cognitive domains. AR-R17779 also reportedly facilitates the induction of hippocampal long term potentiation (LTP), a proposed cellular model for learning and memory, in rats (Hunter, B. E., de Fiebre, C. M., Papke, R. L., Kem, W. R., Meyer, E. M. A novel nicotinic agonist facilitates induction of long-term potentiation in the rat hippocampus. Neurosci. Lett. 1994; 168:130-134).
Despite the beneficial effects of nAChR ligands, it remains uncertain whether chronic treatment with agonists affecting nAChRs may provide suboptimal benefit due to sustained activation and desensitization of the nAChR. In contrast to agonists, administering a nicotinic positive allosteric modulator can reinforce endogenous cholinergic transmission without directly stimulating the target receptor (Albuquerque, E. X., Santos, M. D., Alkondon, M., Pereira, E. F., Maelicke, A. Modulation of nicotinic receptor activity in the central nervous system: A novel approach to the treatment of Alzheimer disease. Alzheimer Dis. Assoc. Disord. 2001; 15 Suppl 1:S19-25). Accordingly, it would be beneficial to target α7 nAChR function by enhancing effects of the endogenous neurotransmitter acetylcholine via positive allosteric modulators that can reinforce the endogenous cholinergic neurotransmission (ACh) without directly activating α7 nAChRs like agonists. Indeed, allosteric modulators for enhancing channel activity have been proven clinically successful for GABAA receptors where benzodiazepines, barbiturates, and neurosteroids behave as allosteric positive modulators acting at distinct sites (Hevers, W., Luddens, H.: The diversity of GABAA receptors. Pharmacological and electrophysiological properties of GABAA channel subtypes. Mol. Neurobiol. 1998; 18:35-86).
To date, only a few nAChR allosteric modulators are known, including: 5-hydroxyindole (5-HI), ivermectin, galantamine, bovine serum albumin, and SLURP-1, a peptide derived from acetylcholinesterase (AChE). Recently, genistein, a kinase inhibitor was reported to increase α7 responses, and PNU-120596, a urea analog, was reported to increase the potency and maximal efficacy of ACh as well as improve auditory gating deficits induced by amphetamine in rats (Hurst, R. S., Hajos, M., Raggenbass, M., Wall, T. M., Higdon, N. R., Lawson, J. A., Rutherford-Root, K. L., Berkenpas, M. B., Hoffmann, W. E., Piotrowski, D. W., Groppi, V. E., Allaman, G., Ogier, R., Bertrand, S., Bertrand, D., Arneric, S. P. A novel positive allosteric modulator of the alpha7 neuronal nicotinic acetylcholine receptor: in vitro and in vivo characterization. J. Neurosci. 2005; 25:4396-405). However, positive allosteric modulator compounds presently known generally demonstrate weak activity, have a range of non-specific effects, or can only achieve limited access to the central nervous system where α7 nAChRs are abundantly expressed.
Accordingly, it would be beneficial to identify and provide new positive allosteric modulator compounds and compositions for treating or preventing conditions associated with α7 nAChRs. It would further be particularly beneficial if such compounds can provide improved efficacy of treatment while reducing adverse effects associated with compounds targeting neuronal nicotinic receptors, for example by selectively modulating α7 nAChRs.